The present disclosure generally relates to functionalized hydrophilic polymeric derivatives that are coated onto a base membrane and subsequently irradiated with a high-energy source to permanently form a hydrophilic surface.
Fluoropolymers such as polytetrafluoroethylene (PTFE) and expanded PTFE (ePTFE) are mechanically robust, high temperature, and chemically inert materials. These advantageous properties are derived from the high strength of the carbon-fluorine bond, which mitigates chemical degradation. Membranes are often formed of porous fluoropolymers because of its chemical inertness and mechanical stability. However, liquid water filtration is problematic due to the hydrophobic property of these types of fluoropolymers and may require treatment to impart hydrophilicity.
Hydrophilicity is defined as the property of being “water loving”. Hydrophilicity is typically used to describe a property of a material or molecule, and typically refers to the ability of the material or molecule to participate in hydrogen bonding with water. Furthermore, hydrophilic materials are typically attracted to, or dissolve well within water. Hydrophilicity may be imparted to an ePTFE membrane by, for example, impregnation using a tetrafluoroethylene/vinyl alcohol copolymer. Such an approach leverages the chemical affinity of the perfluoropolymer in the coating material to the perfluoropolymer of the ePTFE. However, the affinity is sufficiently low that hydrophilicity may be temporary. Other methods include coating the membrane interior of continuous pores with a mixture of a fluoroaliphatic surfactant and a hydrophilic but water insoluble polyurethane. Such an approach may leverage the chemical affinity between the perfluoropolymers to form a two-layer system. In another approach, hydrophilicity of PTFE membrane may be produced by irradiation treatment of the PTFE powdered resin. The resin may be processed with a porogen and virgin PTFE powder to render a microporous PTFE membrane. However, none of the current processes provide permanent hydrophilic properties.
ePTFE membranes may be used for liquid water filtration, but require a pre-wet step generally with alcohols to enable water flow. This results in problematic production considerations as these membranes must be prewetted by membrane manufacturers and shipped wet to end-users. Such a membrane may dewet or dry. The drying of the membrane may render it ineffective and may necessitate, for example, undesirable shipping considerations (such as wet shipping). Other undesirable aspects may include economic considerations such as the need for special handling and sealable containers, and increased shipping weight, and the like.
Accordingly, it would be desirable to provide porous supports having permanent hydrophilic surfaces.